DE2346021A1 - PROCESS FOR THE PRODUCTION OF, 5HEXANDION - Google Patents

Description

Patent attorneys Dipl.-Ing. F. ^ eickmann,

Dipl.-I> to H.Wf.xckmann, D: pl.-Phys. Dr. K. Fincke Dipl.-Ing. F. A. Weickmann, Dipl.-Chem. B. Huber

t MUNICH «6, DEN

POST BOX «60 * 20

MÖHLSTRASSE 22, CALL NUMBER 9139 21/22

289,489 / H / KR

Diamond Shamrock Corporation, 1100 ^ Superior Avenue Cleveland, Ohio 44114, V.St.A.

Process for the preparation of 2,5-hexanedione

The invention relates to the production of 2,5-hexanedione. This compound is an important intermediate for organic synthesis reactions. The invention relates in particular to an improved production process for this compound from the lactone of cO-acetyl-α-cyano-α-hydroxyvaleric acid, which gives technically acceptable yields.

The production of 2,5-hexanedione or acetonylacetone by a multi-stage process, in which monochloroacetone and potassium cyanide are initially reacted with one another , has already been carried out by Romeo Justoni in Gazz. Chim. Ital., 71, pages 41 to 53 and 375 to 388 (1941)

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been. The reaction of monochloroacetone with the cyanide in an alkaline medium gives 2,4-dicyano-5-hydroxy-2,5-dimethyltetrahydrofuran and / or 4-carbamyl-2-cyano-2,5-dimethyl-2,3-dihydrofuran . This product can in turn be reacted, for example with sulfuric acid or hydrochloric acid, to form the lactone of Uj -acetyl- ^ -cyano- ^ -hydroxyvaleric acid. The desired 2,5-hexanedione can then be obtained by hydrolysis of this lactone with an alkali, for example NaOH, with sodium cyanide and carbon dioxide normally being obtained as end by-products.

Carrying out the hydrolysis in the process described above, however, brings only a low yield of the desired 2,5-hexanedione product. The hydrolysis of the lactone using other aqueous bases, for example sodium carbonate, potassium carbonate, sodium bicarbonate or ammonium hydroxide, instead of sodium hydroxide also results in only low product yields, ie up to 50% by weight, based on the lactone used. It is therefore an improved process for the hydrolysis of the lactone of cL * acetyl-1 ^ -cyano-1 "-hydroxyvaleric acid to strive for, which gives larger and technically obtainable yields of 2,5-hexanedione.

It has now been found that when the hydrolysis of the lactone of aC -acetyl- tf ~ - cyano - J ^ -hydr oxy valeric acid with an aqueous base such as sodium carbonate, potassium carbonate and the like, in the presence of a source of Fe ⁺⁺ - Ions, for example iron (II) sulfate, then up to 90-6 of the theoretical yield of the stable 2,5-hexanedione product can be obtained.

As already stated, it is already known that 2, Ü <hexanedione by removing the lactone from σ6-acetyl -

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ic _-

% -cyano- Jf -hydroxyvaleric acid hydrolyzed with an equimolar amount of an aqueous base (50% NaOH) according to the following reaction scheme:

NA / ^CH 3

o c α .ο ο

η ι t ν. η η

H ₃ CC-CH CHg ¹ * + NaOH- »CH ₃ -C-CH ₂ -CH ₂ -C-CH ₃ + CO ₂ + NaCl-i

(2,5 hexandiori)

In this reaction, the lactone is first converted into cyanohydrin after hydrolysis, which in turn is split in the presence of alkali and converted to 06 -acetonylacetoacetic acid by splitting off hydrocyanic acid (HCW). The acetonylacetoacetic acid then decarboxylates easily to 2,5-hexanedione and carbon dioxide (CO ₂ ), while the hydrocyanic acid reacts with sodium hydroxide to form sodium cyanide.

In an aqueous solution at moderately elevated temperatures and in particular in the presence of CO ₂ , however, the sodium cyanide decomposes rapidly with the formation of free hydrocyanic acid. The free hydrocyanic acid then reacts with the 2,5-hexanedione product, which significantly reduces the overall yield of this product.

The lactone starting product is prepared in such a way that monochloroacetone is first condensed with sodium cyanide and then the resulting cyclic product 2,4-dicyano-5-hydroxy-2,5-dimethyltetrahydrofuran and / or'4-carbamyl-2- cyano-2,5 ~ dimethyl-2,3-dihydrofuran hydrolyzed by the action of hydrochloric acid. These reactions and the resulting products are already in the aforementioned Justoni article

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and do not form part of this invention.

According to the present invention, it is now available so that it hydrolyzes the lactone of JU-acetyl ^ ^ cyano-hydroxyvaleric acid in a conventional manner with aqueous alkali, but with the exception that the reaction is carried out in the presence of a compound , which ^{supplies Fe ++} ions, iron (II) sulfate is currently particularly preferred as the source for these ions. For this reason and because of the ready availability of this compound and its cheapness, the further description of this invention will be given in terms of ferrous sulfate.

During the process according to the invention, to the extent that hydrogen cyanide is released, the ^{compound which supplies Fe ++} ions, for example iron (II) sulfate, lowers this compound formed as a by-product. A reaction with the cyanide group of the acid takes place, whereby a stable complex, namely a ferrocyanide ion complex, is formed, whereby the hydrogen cyanide is intercepted for the further reaction with the diketone product.

The amount of ferrous sulfate used in the present invention can generally be from about 0.05 mol to about 0.75 mol vary per mole of lactone. The amount of alkali compound, for example, sodium carbonate, potassium carbonate and the like, which can be suitably used generally from about 0.2 moles to 2 moles per mole of the lactone. The use of larger amounts of the alkali compound would ordinarily cause excessive foaming in the reaction mixture. It has shown, that amounts of ferrous sulfate in the range of about 0.15 Moles to 0.60 moles and especially from 0.30 moles to 0.50 moles

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in combination with alkali amounts of about 0.5 mole "to 1 mole per mole of the lactone give optimal results of the desired product 2,5-hexanedione, at the same time the product is very effectively stabilized against significant degradation even over prolonged reaction times.

The method of the invention can be generally carried out at temperatures of about 40 to 100 ⁰ C. The reaction rate seems to be somewhat pH-sensitive, so that the reaction time in the specified temperature range, depending on the amount of iron (II) sulfate used and the ratio of iron (II) sulfate to alkali compound used, from about 1 hour to. varies approximately more than 6 hours.

The order in which the starting materials are added is not particularly critical. However, it is preferred to use ferrous sulfate to be added at the beginning of the reaction in order to utilize its interception properties as effectively as possible.

After the reaction has ended, the reaction mixture is cooled to room temperature and the hexanedione is isolated therefrom by solvent extraction. Suitable solvents for this purpose are, for example, toluene, ethyl acetate, chloroform and tetrachlorethylene. Alternatively, the hexanedione product can also be used further in some cases without isolation, for example for the production of other organic compounds such as 2,5-dimethylpyrrole. In this procedure, the reaction mixture is cooled ^{to about 40 °} C. after the production reaction for the hexanedione has ended. Gaseous ammonia is then blown into the reaction mixture until the resulting

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exothermic reaction has ended. The dimethylpyrrole product separates out of the aqueous phase and becomes from it isolated. At the end it is purified by distillation.

The process according to the invention is an economical, easy to carry out process for the industrial production of 2,5-hexanedione from the lactone of d, -acetyl- ^ ~ cyano-y-hydroxyvaleric acid. This is in particular due to the fact that the scavenger compound used, iron (Ii) sulfate, which is cheap and readily available.

The process according to the invention also provides a stable ferrocyanide salt, which is non-toxic, as a by-product and that does not cause any difficult warping and / or pollution problems. On the other hand fall at chemicals that pollute this process unless ferrous sulfate is used.

The invention is illustrated in the examples. All information regarding the quantities, proportions and percentages are based on weight.

example 1

A. Production of the lactone from co-acetyl - ^ - cyano-y-hydroxyvaleric acid:

A 200 ml three-necked flask equipped with a stirrer, thermometer, condenser, dropping funnel and heating mantle is filled with 73 ml of water. With stirring g (0.145 mol) of crude are in the piston 24.1 2,4-dicyano-5-hydroxy-2, 5 ~ dimethyltetrahydrofuran and / or 4-carbamoyl-2-cyano-2,5 ~ dimethyl-2,3 ~ dihydrofuran (melting point 177 to 179 ⁰ C) given. The resulting slurry will

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12.4 ml of concentrated HCl are quickly added, whereupon the reaction mixture is ^{stirred at a controlled temperature of 30 °} C. for 15 to 30 minutes. The reaction mixture is then ^{cooled to 15 °} C. and the solid product is isolated, washed with cold water and dried. Which is obtained with a yield of 99%, the product has a melting point of 71-72 ⁰ C. The vapor phase chromatography shows that the product contains at the desired lactone & approximately 98i.

B. Production of 2,5-hexanedione:

Anhydrous sodium carbonate (3.2 g - 0.03 mol) is dissolved in 60 ml of water in the reaction flask. To this 3.9 g of dried iron (II) sulfate, which contains 87% anhydrous iron (II) sulfate (0.0223 mol), and 10.0 g (0.059 mol) of the lactone product obtained in Part A are added. The resulting slurry is stirred ^{to 71 ° C. with slow heating.} During this period some foaming occurs in the reaction mixture. The reaction temperature is then increased to 88 ° C. and the reaction is continued at this temperature for 6 1/3 hours. After cooling, the reaction mixture is filtered and the percentage of the 2,5-hexanedione product obtained is measured by vapor phase chromatography. This uses a flame ionization detector and an external standard. The solvent is water. It is found that the 2,5-hexanedione is obtained in a yield of 89-6.

Examples 2 to 4

These examples show the stabilizing effect of iron (II) sulfate on the overall synthesis reaction, which itself

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takes place with extended reaction times. This allows good practical yields of the 2,5-hexanedione product can be obtained. A series of experiments is carried out according to the general procedure of Example 1 (B), wherein varying molar per mole of the starting lactone product Concentrations of iron (II) sulfate according to the information in in the table below can be used. In these experiments, anhydrous sodium carbonate (NapCO,) is used as the base used at a concentration of 0.5 per mole of the lactone. The following results are obtained:

At- FeSO. Reaction reaction hexanedione yield game (mol; temperature time %

( ⁶ C) min

2 0.0635 68-73 110 75

3 0.127 77 135 76 h 0.264 80 170 77

These results show that if the reaction is continued, no degradation of the product takes place even at elevated temperatures if iron (II) sulfate is present in the reaction mixture in the stated amounts. The use of an iron (II) sulfate concentration of 0.380 mol per mol of the lactone at a temperature of 88 ⁰ C over a period of 380 min (reaction of Example 1) gives an overall product yield of $ 89.

These results are in contrast to those obtained when the lactone hydrolysis is carried out in the absence of ferrous sulfate. If, as in Example 2, the reaction is carried out at 69 ^° C., but this component is excluded, then when analyzing an aliquot of the reaction mixture by vapor phase

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Chromatography 70 min after the start of the reaction that the investigated product contains 6b% hexanedione. If the reaction continues, however, periodic analysis of the reaction mixture shows a progressive reduction. the hexanedione content of the product. For example, an analysis of the reaction mixture after carrying out the above-described reaction for a further 35 to 40 minutes shows a hexanedione content of about 12% less than in the previous analysis.

Example 5

The reaction of Example 1 is repeated at 67 ° C, wherein the addition of iron (II) sulfate (0.380 mol per mol of lactone) is postponed up to 1 hour after the start of the reaction will. The total reaction time is 310 min. The yield of the hexanedione product obtained is 73? Ό and is thus lower than the yield according to Example 1. This indicates that iron (II) sulfate is best for achieving this Product yields are more effective when it is already present in the reaction mixture at the beginning.

Example 6

The procedure is as in Example 1, except that 1.0 mol of sodium carbonate is used instead of 0.5 mol per mol of lactone will. Some foaming is observed during the reaction. After implementation The reaction mixture is analyzed by vapor phase chromatography for about 3 hours at 75 ° C. It is found that the product contains 73 / ό 2,5-hexanedione.

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Claims (6)

Claims 1. A process for the preparation of 2,5-hexanedione by hydrolysis of the lactone of <& -acetyl- jf-cyBno- / hydroxyvaleric acid with aqueous alkali, characterized in that the hydrolysis reaction is carried out in the presence of a source of Fe ⁺⁺ ions, such as iron (II) sulfate, which reacts with the hydrogen cyanide formed to form a stable ferrocyanide complex, which prevents further reaction of the acid with the 2,5-hexanedione product and its degradation. 2. The method according to claim 1, characterized in that the alkali compound is sodium hydroxide, Sodium carbonate and / or potassium carbonate are used. 3. The method according to any one of claims 1 to 2, characterized characterized in that about 0.05 mol to about 0.75 mol of iron (II) sulfate per mole of the lactone starting material used. 4. The method according to any one of claims 1 to 3, characterized in that about 0.2 mol to 2 moles of alkali are used per mole of the starting lactone compound. 5. The method according to any one of claims 1 to 4, characterized in that the reaction is carried out at temperatures of 40 to 100 ⁰ C over periods of about 1 hour to more than 6 hours. 6. The method according to any one of claims 1 to 5, characterized in that the iron (II) sulfate incorporated into the roaction mixture at the beginning of the implementation. ' 409812/1229